BVG Door Closure Alarm for FSN 423

A small soundmod for Frankfurt - Wiesbaden's 423, changing the door alarm soundset to the one you typically hear on Berlin's subway trains.

The following changes have been made:

• changed default door closure beeping
• added loud external alarm
• removed long door opening beep

This mod fully works with the 423 soundmod, as it loads above said soundmod and by that the door sounds of this mod are prioritized.